Microsoft's Bing Search API won't be free much longer. The company plans to offer the API through the Windows Azure Marketplace for monthly subscription fees beginning at "approximately" $40 for up to 20,000 queries each month. The transition will begin sometime over the next several weeks and "will take a few months to complete." In the meantime, developers can try the API for free. Specifics on the transition timeline, pricing and other details will be released soon. Says Microsoft:

(Developers) can expect the transition to involve targeting a new API end point, moderate changes to the request and response schemas, and a new security requirement to authenticate your application key. Developers using approximately 3 to 4 million queries and above can expect to transition through a separate process (details will be provided shortly).

Ars Technica notes that the Bing API's price points are pretty good compared to Google's: $5 per 1,000 queries, 100 a day free. Bing's still in the back seat when it comes to market share, as I suspect everyone knows. comScore estimates its share is about 15 percent, compared to Google's 66 percent.